1. Field of the Invention
The present invention relates to a communication control device which controls communication performed over a communication line.
2. Description of the Related Art
Traditionally, input/output devices (each hereinafter called an I/O device) such as communication control devices connected to a computer have had be designed to match the system bus internal to the computer, and a change in the system bus architecture has required an overall change in the design of the I/O devices.
Further, when the system configuration is fixed, if the system is to be constructed in a dual configuration for enhanced reliability, a large-scale configuration has had to be employed, requiring, for example, complete duplication of the computer itself.
On the other hand, in the field of personal computers (PCs), USB (Universal Serial Bus) and IEEE 1394 have been standardized in recent years as interface standards for interfacing peripheral devices to personal computers. These are next-generation serial interfaces that are expected to replace the traditional RS232C, and support “Hot Plug In”, “Plug and Play”, “Isochronous Transfer”, etc.
“Hot Plug In” is a function that enables a device to be connected without having to turn the system off, while “Plug and Play” is a function by which a device is just connected to a personal computer and is automatically configured to be ready for use without going through cumbersome installation procedures. Further, isochronous transfer makes possible, for example, the transmission of audio and video signals that cannot tolerate dropouts, by guaranteeing transmission bandwidth and giving higher data transmission priority.